Method of implanting joint prosthesis with infinitely positionable head

ABSTRACT

A method for preparing an articulating component of a joint prosthesis having an implant engaged within a bone of the joint, the method including inserting a first articulating component into a first insert in the implant within the bone of the joint, determining an angular orientation of the inserted first articulating component relative to the implant within the bone of the joint, positioning a second articulating component within a second insert component, replicating the angular orientation of the first articulating component in the second articulating component positioned within the second insert, fixing the second articulating component to the second insert component at the replicated angular orientation, and mounting the second insert component with the fixed second articulating component to the implant engaged within the bone of the joint.

This is a divisional application of U.S. application Ser. No. 13/874,025filed Apr. 30, 2013, which issued as U.S. Pat. No. 9,132,012 on Sep. 15,2015, which is a divisional of U.S. application Ser. No. 11/025,185filed Dec. 29, 2004 which issued as U.S. Pat. No. 8,444,698 on May 21,2013, the entire contents of which are each herein incorporated byreference.

This application is related to U.S. Pat. No. 8,562,686 which issued Oct.22, 2013.

BACKGROUND OF THE INVENTION

The present invention relates to joint prosthesis, and particularly toprosthesis having an articulating head component. More specifically, theinvention relates to a system for achieving infinitely variablepositions for the head component relative to a bone engaging portion ofthe prosthesis.

Repair and replacement of human joints, such as the knee, shoulder,elbow and hip, has become a more and more frequent medical treatment.Longer life spans mean that the joints endure more wear and tear. Moresports activities mean greater likelihood of serious joint injuries.Treatment of injuries, wear and disease in human joints has progressedfrom the use of orthotics to mask the problem, to fusion of the joint,to the use of prostheses to replace the damaged joint component(s).

As the success rate for total or partial joint replacements hasincreased, so too has the need for modularity and universality in thejoint prosthesis. Patient variety means that no single size orconfiguration of joint prosthesis will suffice. The physical dimensionsof a patient's joint components vary, as well as the bio-mechanicrelationship between these components. For instance, in a shoulderprosthesis, the relationship between the articulating humeral andglenoid components can be significantly different between patients.These relationships are especially important where only one component ofthe joint is being replaced and must integrate with the existing naturalopposing joint component.

In joint replacement procedures, the proximal end of a bone, such as thehumerus, is resected to form a stable platform to receive a jointimplant. In some cases, it is discovered after the implant has beenfixed within the bone that the resection was inappropriate for thepatient's joint. Correction of this problem requires, at a minimum,removal of the implant and implantation of a new implant to fit theresected surface. The availability of a differently sized or configuredimplant component is very beneficial, and even more important wherefurther resection of the bone is necessary.

For instance, in many shoulder surgeries, only the humeral component isreplaced, leaving the glenoid component intact. In this case, it isimperative that the articulating surface of the humeral component matchthe articulating surface of the glenoid component as perfectly aspossible, both statically and dynamically. With a typical humeralprosthesis, version and inclination are adjusted by the geometry of thehead of the prosthesis. In other words, certain pre-determined headgeometries are available that can be selected for a mating glenoidcomponent. Absent an infinite variety of pre-determined head geometries,the resulting humeral prosthesis can often only achieve a best-fitrelationship to the glenoid component of the shoulder joint.

In a typical surgical procedure, a trial component will be used todetermine the optimum final component to be fixed to the bone. In mostcases, the surgeon is able to make a good selection that fits the jointvery well. However, in some cases, the accuracy of the fit cannot bedetermined until the surgery is completed and the patient has had anopportunity to exercise the repaired joint. Where significantly problemsarise, a revision surgery may be necessary to replace an improperlysized or configured joint component. One typical revision surgeryrequires removal of the entire prosthesis from the bone and replacementwith a different prosthesis.

There is a significant need for a joint prosthesis that is both modularand universal. Such a prosthesis would be easily manipulated during thesurgery and capable of achieving nearly infinite version and inclinationangles. Moreover, an optimum prosthesis would be readily available formodification in a revision surgery without having to remove the entireprosthesis.

SUMMARY OF THE INVENTION

These and other needs of the prior art are met by the present inventionin which a joint prosthesis includes a removable component to which thearticulating component of the prosthesis is connected. The removablecomponent permits adjustment of the angular orientation of thearticulating component so that the joint prosthesis is truly universal.

In one aspect of the invention, the joint prosthesis includes acomponent configured for engagement within the bone of a patient, suchas in a prepared intramedullary canal. The component, or stem, can beconfigured as a trial stem or as a permanent implant. The proximal endof the stem includes a platform surface which defines features forremovably supporting a removable insert component. A fixation element isprovided that is used to fix the insert component to the stem. Inaccordance with one embodiment of the invention, the fixation element isitself removable, although it is capable of achieving substantiallypermanent, rigid fixation of the insert component to the stem.

The joint prosthesis includes a mating component that has one portionconfigured to mate with the articulating component and another portionconfigured to adjustably mate with the insert component. The matingcomponent is also provided with a bore to permit access to the fixationelement when the mating component is mated with the insert component, toallow removal of the fixation element and thereby removal of the insertcomponent from the stem with the mating component intact.

In a specific embodiment of the invention, the insert component includesa plate portion and a base portion projecting from the plate portion.The insert component defines a tapered bore therethrough and a fastenerbore through the bottom wall of the base portion. The platform surfaceof the stem defines an insert cavity configured to receive the entireinsert component therein. In particular, the insert cavity includes abase recess into which the insert base portion snugly fits, and a platerecess for receiving the plate portion. Preferably, the plate recess isopen at one edge of the platform surface to facilitate access to theplate portion of the insert component and ultimately to facilitatedislodgement of the insert component from the insert cavity.

The mating component includes a ball portion that is configured to forma press-fit within the tapered bore of the insert component. The matingcomponent also includes a tapered cylinder configured to mate with acomplementary bore defined in the articulating component or head. Bothends of the mating component are therefor configured for a press-fitengagement accomplished by use of a typical impaction tool.

In accordance with a method of the present invention, a joint prosthesisis constructed by placing an insert component into a complementaryconfigured cavity defined in the proximal portion of a bone engagingimplant, such as a stem. A fixation element, such as a screw, is used tofix the insert within the stem. A mating component is engaged with theinsert component, such as by a press-fit engagement between a taperedbore in the insert and a compressible ball portion on the matingcomponent. An articulating component, such as a femoral head, is thenmated with the mating component, such as through a press-fit engagement.

In a further feature of the present invention, a revision procedureincludes the step of accessing the fixation element through openingsdefined in at least the mating component. The fixation element isreleased from engagement with the stem so that the insert component isno longer fastened thereto. The insert component is then removed,preferably with the mating component and head components fastenedundisturbed.

In yet another aspect, the removed insert component with the undisturbedmating component and head component can be transported to a replicationinstrument. The angular position of at least the mating component may beascertained relative to a fixed datum using the instrument. That angularposition can be conveyed to a new insert and mating component using theinstrument. Once the three-dimensional angles have been properlyreplicated in the new prosthesis components, the mating component can befixed within the insert component, preferably by impaction. The headcomponent may also be engaged to the mating component, also preferablyby impaction. The completed assembly is then conveyed to the stem thathas not been removed from the patient's bone. The insert component isplaced within the insert cavity in the stem and the fixation element isused to rigidly connect the insert component to the stem with the matingcomponent and head component in their proper anatomic relation to thepatient's bone. These steps can be implemented in a true revisionsurgery to replace an existing prosthesis, or can be carried out duringan original joint replacement procedure.

In a further aspect, a method for preparing an articulating component ofa joint prosthesis having an implant engaged within a bone of the joint,the method including inserting a first articulating component into afirst insert in the implant within the bone of the joint, determining anangular orientation of the inserted first articulating componentrelative to the implant within the bone of the joint, positioning asecond articulating component within a second insert component,replicating the angular orientation of the first articulating componentin the second articulating component positioned within the secondinsert, fixing the second articulating component to the second insertcomponent at the replicated angular orientation, and mounting the secondinsert component with the fixed second articulating component to theimplant engaged within the bone of the joint.

It is one object of the invention to provide a joint prosthesis that isboth modular and universal. This object is achieved by features thatpermit infinitely variable positioning of a mating joint componentrelative to a bone engaging portion of the prosthesis.

Another object is to provide a prosthesis that is readily available formodification, whether during initial implantation or during a subsequentrevision procedure. One benefit of the invention is that thismodification can occur without removing or disturbing the bone engagingcomponent, or stem, of the implant.

These and other objects and benefits of the invention will beappreciated upon consideration of the following written descriptiontogether with the accompanying figures.

DESCRIPTION OF THE FIGURES

FIG. 1 is a side view of a prior art humeral prosthesis.

FIG. 2 is an enlarged cross-sectional view of a portion of a jointprosthesis with a mounting element configured for articulatingengagement with the stem of the prosthesis to permit angular positioningof a head component in multiple degrees of freedom.

FIG. 3 is a side exploded view of a modular prosthesis in accordancewith one embodiment of the present invention that is adapted tofacilitate modification or revision of the implant.

FIG. 4 is a front cross-section view of the modular prosthesis shown inFIG. 3 in an assembled configuration.

FIG. 5 is a front perspective of a stem component of the modularprosthesis shown in FIGS. 3-4.

FIG. 6 is an enlarged cross-section view of a portion of the stemdepicted in FIG. 5.

FIG. 7 is a top perspective view of an insert component of the modularprosthesis illustrated in FIGS. 3-4.

FIG. 8 is a side cross-section view of the insert component shown inFIG. 7.

FIG. 9 is a side cross-section view of a mating component of the modularprosthesis shown in FIGS. 3-4.

FIG. 10 is a side view of a fixation component of the modular prosthesisshown in FIGS. 3-4.

FIG. 11 is a side view of a replication instrument for use inreplicating the orientation of the mating component of the prosthesisshown in FIGS. 3-4.

FIG. 12 is a perspective view of a dummy stem for use in the replicationinstrument shown in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and described in the following written specification. It isunderstood that no limitation to the scope of the invention is therebyintended. It is further understood that the present invention includesany alterations and modifications to the illustrated embodiments andincludes further applications of the principles of the invention aswould normally occur to one skilled in the art to which this inventionpertains.

The present invention contemplates a joint prosthesis with anarticulating component that must be positioned at a particular angularorientation to replicate and accommodate anatomic features of thepatient's joint. In the following description, the prosthesis isidentified as a humeral prosthesis for a shoulder implant. It isunderstood, however, that the principles of this invention can beapplied to other prosthesis that include an adjustable component. Thepresent invention is particularly suited for prostheses that areamenable to replacement or adjustment in a revision surgery.

By way of background, a typical joint prosthesis of the prior art isillustrated in FIG. 1. The prosthesis 10 is the humeral component of ashoulder prosthesis that can be implanted in the humerus bone forarticulating engagement with the natural glenoid or with a glenoidprosthesis. The prosthesis 10 includes a stem 12 configured to beimplanted within the humerus bone in a conventional manner. The stem 12forms a platform surface 15 that faces the glenoid component of thejoint when the prosthesis is in its operative position. The platformsurface 15 defines a tapered bore for use in mounting the articulatinghead component 14. The head component includes a tapered post 18 thatcan be press-fit or friction-fit within the tapered bore 16 to firmlymount the head component to the stem 12.

The prosthesis 10 can be a modular prosthesis, meaning that a number ofstem and head geometries can be provided from which a selection can bemade that most closely approximates the natural joint components of thepatient. Thus, the angle of the platform surface 15 can be differentamong stems 12. While all head components 14 will include a generallyspherical bearing surface 19, the orientation of this surface relativeto the platform surface 15 can be changed. Specifically, the location ofthe post 18 relative to the bearing surface 19 can be offset from thecenter of the surface (i.e., an eccentric head). In some cases, theangle of the post can be different between head components 14.

An improved modular prosthesis introduces an articulating mountingelement 30 between the stem 12 and a head component 20, as shown in FIG.2. This mounting element 30 is shown and described in co-pendingapplication Ser. No. 10/748,448 (the '448 application), entitled JOINTPROSTHESIS WITH INFINITELY POSITIONABLE HEAD, filed on Dec. 30, 2003,and owned by the assignee of the present invention. While the '448application provides a more detailed disclosure of the mounting element,which disclosure is incorporated herein by reference, following is ageneral description to facilitate an understanding of the presentinvention.

This mounting element 30 of the '448 application includes a proximalportion 33 that mates with the head component 20. In a specificembodiment, the proximal portion 33 defines a tapered surface that ispress-fit or friction-fit within a complementary bore 21 defined in thehead component.

The mounting element 30 further includes an articulating portion 34 thatis preferably in the form of a spherical ball joint. The articulatingportion is sized to achieve a press-fit engagement within a tapered bore16 of the stem 12 when the portion 34 is pushed sufficiently far intothe bore. The spherical shape of the articulating portion 34 allows themounting element 30 to rotate about three dimensional axes x, y, z.Thus, the mounting element can rotate about its own axis (the x axis),pivot about a version axis (the y axis) or pivot about an inclinationaxis (the z axis).

In addition to the press-fit engagement, a second fixation capability isdisclosed in the '448 application that augments the engagement betweenthe articulating portion 34 and the tapered bore 16. In particular, amachine screw 40 may be provided that includes a threaded portion 46configured to mate with a threaded bore 18 in the stem 12. The bore 18is concentrically disposed at the base of the tapered bore 16. The screw40 is introduced into the threaded bore 18 through the articulatingmounting element 30.

As shown in FIG. 2, the mounting element 30 defines a central passageway36 that extends through the length of element and that is open at itsproximal and distal ends. The passageway defines an internal bearingsurface 38 at the distal end of the element, or more specifically at thebase of the articulating portion 34. The screw includes a head 42 thatincludes an underside surface 44 that is complementary with the internalbearing surface. These two surfaces form a spherical bearing interfacethat allows the mounting element 30 to experience its full range ofangular motion without interference from the screw 40, even when thescrew is loosely threaded into the threaded bore 18. The articulatingportion 34 defines a relief 39 at the distal end of the passageway 36 tofacilitate this full range of movement of the mounting element.

The passageway 36 in the mounting element allows introduction of thescrew 40 through the mounting element and into the threaded bore 18. Thescrew can be loosely threaded into the bore to permit movement of themounting element. Once the proper position for the mounting element 30has been achieved, the screw can be tightened using a tool engagedwithin the tool recess 43 on the head 42 of the screw. As the screw istightened, it drives the articulating portion 34 deeper into the angledbore 16, thereby fixing the mounting element against furtherarticulation. The screw thus combines with the friction or press-fitfeature to lock the construct.

The mounting element 30 disclosed in the '448 application represents asignificant improvement over the prior art prosthesis 10 in that itgreatly simplifies the process of aligning the mounting element, andultimately the humeral head, at the proper anatomic angle for thepatient's shoulder joint. Moreover, the mounting element 30 allowsinfinite positioning of the humeral head, in lieu of the limitedselection of pre-defined angles available with the prosthesis of theprior art.

Even though the mounting element 30 presents a significant advance overthe prior prostheses, problems still arise when a revision surgery isindicated. During some primary implant procedures, the surgeon maydiscover that a different humeral head is needed after the final implantstem has been fixed within the humerus. In some cases, the accuracy ofthe fit of the prosthetic components cannot be determined until thesurgery is completed and the patient has had an opportunity to exercisethe repaired joint. Where significant problems arise, a revision surgerymay be necessary long after the primary surgery to replace an improperlysized or configured joint component. In most cases, the modularcomponents of the prosthesis cannot be removed without also removing thecomponent, or stem, fixed within the bone. Removal and replacement of animplanted stem is often problematic and runs the risk of creating arevision construct of poor integrity.

The present invention addresses the problem of revision surgeries onprosthetic implants by providing an insert component that allows thebone implanted component to remain within the bone. In accordance withone embodiment of the invention, a prosthesis 50 is provided asillustrated in FIGS. 3-4 that includes a stem 52, an insert component54, a fixation element 56 and a mating component 58. The stem 52 isconfigured to be implanted within a bone of a patient and may beidentical in most respects to prior stems used for similar jointreplacement procedures. More particularly, the portion of the stem 52that is implanted within the prepared intramedullary canal of thehumerus may be identical to the prior art stem 12 shown in FIG. 1. Aswith the prior art stems, the stem 52 includes a platform surface 60that is aligned toward the mating aspect of the joint, or the glenoidaspect in the case of a shoulder prosthesis.

However, the platform surface 60 of the stem 50 in the present inventiontakes on different characteristics from the prior art. In particular,the platform surface is configured to receive an insert component 54 anda fixation element 56 operable to rigidly fix the insert component tothe stem. The insert component 54 is adapted for engagement with themating component 58 under conditions that allow adjustment of theangular orientation of that component. The mating component 58 isconfigured to receive an articulating component, such as the humeralhead 20 shown in FIG. 2.

Referring to FIGS. 5-6, details of the platform surface 60 of the stem50 are illustrated. The platform surface defines an insert cavity 62with a base recess 64 embedded within the stem and a plate recess 66opening into the platform surface. As shown in FIG. 5, the base recess64 is preferably cylindrical, for ease of manufacturing and tofacilitate placement of the insert component 54 within the insert cavity62. However, other cross-sectional configurations for the base recessmay be acceptable.

The plate recess 66 is generally rectangular with an edge 67 that opensat the superior end 61 of the platform surface 60. The plate recesspreferably includes a rounded inboard end to facilitate manufacture ofthe recess 66. For instance, the base recess 64 can be formed bydrilling to a certain depth into the platform surface 60 of the stem 52.The plate recess 66 can be initially formed by drilling concentricallywith the base recess, but at a larger diameter and to a shallower depth.The platform surface can then be milled to carve out the open edge 67 ofthe plate recess.

The insert component 54 is configured to fit snugly within the insertcavity 62, as can be seen from FIGS. 7-8. In particular, the insertcomponent includes a base portion 70 that is configured to be snuglyreceived within the base recess 64. Thus, the cross section of the baseportion preferably emulates the cross section of the base recess—i.e.,the base portion 70 is cylindrical in the illustrated embodiment. Theinsert component further includes a plate portion 72 that is alsoconfigured to be snugly received within the plate recess 66. As with thebase portion, the plate portion 72 follows the configuration of theplate recess 66 so that the base portion is generally rectangular with arounded inner edge. In the preferred embodiment, the plate portion 54includes a tab 80 that extends from the cylindrical base portion 70 sothat the free end 81 of the tab is accessible at the open edge 67 of theplate recess. Preferably, the free end 81 is substantially coincidentwith the open edge.

The plate portion 72 defines a lower surface 78 that rests within theplate recess 66. The insert component is preferably sized so that thebase portion 70 is slightly offset from the bottom wall 77 of the baserecess 64 when the lower surface 78 of the plate portion 72 is situatedwithin the plate recess. The free end 81 of the plate portion 72includes a lower rounded edge 79 to provide a small access for a removaltool between the insert component and the insert cavity, as discussed inmore detail herein.

In one feature of the invention, the insert component 54 defines atapered bore 74. The tapered bore mates in press-fit engagement withengagement surface 85 of a ball portion 84 of the mating component 58(FIG. 9). This press-fit engagement accomplishes final fixation of themating component 58 with the stem 52. This interface may be similar tothe press-fit engagement described in the '448 application incorporatedby reference. The mating component preferably includes a taperedcylinder 82 that is configured for press-fit engagement within thecomplementary bore 21 of the humeral head 20 (also shown in FIG. 2). Themating component includes a central bore 87 that may be configured for apress-fit engagement with a male feature on the humeral head, in lieu ofor in addition to the press-fit against the outer surface of the taperedcylinder 82.

In order to secure the mating component to the stem 52, a fixationelement 56 is provided that fixes the insert component 54 to the stem.In the preferred embodiment, the insert cavity 62 of the stem defines athreaded bore 68 in the base recess 64. The fixation element 56constitutes a screw, as shown in FIG. 10, with a threaded stem 92adapted to engage the threaded bore 68. The head 94 of the screwpreferably includes a hex recess 96 for receiving a hex driving tool ofknown design. The insert component 54 includes a fastener bore 76through the bottom wall 77 of the component to receive the fastenertherethrough. Thus, the insert component is fixed to the stem 52 usingthe fixation element or screw 56, as shown in FIG. 4. The ball portion84 of the mating component 58 preferably defines a flared opening 89 toprevent contact between the mating component and the head of the screwwhen the mating component 58 is impacted within the tapered bore 74.

The fixation element 56 represents one beneficial feature of theprosthesis 50 of the present invention. Specifically, the fixationelement allows removal of the insert component 54 from the prosthesisstem 52 at any time, including when the mating component 56 is in solidengagement with the insert component. This feature facilitates revisionof the articulating component, or humeral head, at any time by simplyunscrewing the fixation element 56 from the threaded bore 68 in thestem. When the fixation element 56 is removed, the insert component 54can be readily extracted from the insert cavity 62 in the stem.Preferably, a tool can be pressed between the rounded edge 79 of the tabportion 80 of the insert component and the platform surface 60 of thestem to help dislodge the insert without contacting the mating component58. Once removed, the insert component and mating component can serve asa trial component that is replicated in a final prosthesis.

Whether as a final implant or a trial implant, when the mating portion58 is installed in the tapered bore 74, the ball portion 84 may beinitially loosely situated within the bore 74 so that the angularorientation of the mating component 58 can be adjusted. This adjustmentmay occur with the articulating head component 20 mounted on the matingcomponent. Once the proper angles have been determined, the matingcomponent can be fixed within the tapered bore by impaction in a knownmanner, and the humeral head can be added in a similar fashion. It canbe appreciated that since the mating component is engaging a removableinsert component 54 the impaction steps may occur apart from the implantstem 52. Thus, the impaction of the mating component into the insertcomponent, and the impaction of the articulating head onto the matingcomponent can occur on a fixture. Rigid fixation of the final implantmay be accomplished through means other than impaction, but thisfixation may still occur apart from the stem implanted within thepatient's bone.

Preferably, the adjustment of the angular position of the matingcomponent for use in a final prosthesis can occur using a replicationinstrument, such as the instrument disclosed in co-pending applicationSer. No. 10/879,261 (the '261 application), entitled INSTRUMENTATION FORRECORDING AND REPLICATING ORTHOPAEDIC IMPLANT ORIENTATION, owned by theassignee of the present invention, the disclosure of which isincorporated herein by reference.

While details of the instrument are found in the '261 application,following is a general description of the instrument 100 as depicted inFIG. 11. In particular, the instrument includes a base assembly 102 thatcarries a stationary clamp element 104 and a movable clamp element 106.An adjustment mechanism 108 may be manually operated to move the movableclamp element toward the stationary element 104. The neck of theprosthesis stem 52 is provided with positioning grooves 53 a and 53 b.The superior groove 53 a accepts the fixed clamp element 104, while apair of inferior grooves 53 b are configured to mate with the movableclamp element 106. When the neck of the stem is engaged by the clampelements 104, 106, a fixed datum D is established that is perpendicularto the platform surface 60. The spatial angular orientation of themating component 58 is gauged relative to this datum. The base assembly102 thus establishes a fixed spatial position for this datum that can beused to replicate the angles of the mating component.

To achieve this replication, the instrument 100 further includes areplication fixture 110 that is mounted on the base assembly 102. Thefixture includes a platform 112 with legs 114 that are supported on thebase assembly. The platform 110 includes an annular dome 116 whichsupports a spherical washer 118 on one surface and a cannulated guidemember 120 on the opposite surface. The guide member includes a hollowstem portion 121 that passes through the dome 116 and washer 118. Thestem portion 121 is threaded to receive a locking nut 122 to fix theangular orientation of the guide member 120 relative to the datum D.

As explained in more detail in the '261 application, the guide member120 cannula allows passage of an alignment tool 125, and moreparticularly the guide shaft 127 of the tool. The distal end of theguide shaft is sized to fit snugly within the bore 87 of the taperedcylinder 58. When the guide shaft 127 is situated within the cylinder ofthe mating component used as part of the trial assembly, the guidemember 120 and spherical washer 118 assume a corresponding spatial anglerelative to the dome 116. At this point in the method, the locking nutis tightened, thereby fixing the three-dimensional angular position ofthe guide member 120. The replication fixture 110 is then removed andstem 52 is released from the base assembly. A final humeral prosthesisconfigured as the prosthesis 50 shown in FIGS. 3-4 may then clampedwithin the base assembly with a final mating element 58 loosely engagedwithin the tapered bore 74 of a final insert component 54. The alignmenttool is reinserted into the guide member and the guide shaft is engagedwith the mating component to replicate the angular orientation of thetrial component. The alignment tool 125 is configured with an impactionend 129 that can be struck with a mallet to impact the mating elementinto the insert component to form the replicated final construct. Oncethe humeral head is impacted onto the mating component, the insertcomponent can be positioned within the insert cavity 62 of a stem 52implanted within the prepared intramedullary canal of the patient'sbone. The insert component is then fixed in place using the fixationelement 56.

As shown in FIG. 11, the replication instrument 100 engages a prosthesis50 that can be configured as a final or a trial prosthesis. However, forthe purposes of providing a baseline for replicating the angularorientation of the articulating components of the joint, an entire boneimplant is not necessary. Thus, in an alternative method for replicatingthe necessary angles, a dummy prosthesis 150 is provided as shown inFIG. 12. The dummy prosthesis 150 meticulously emulates the proximalportion of the trial or final prosthesis 50 to provide the properalignment of the datum line D (FIG. 11). Thus, the dummy prosthesisincludes a truncated stem 152 that includes positioning grooves 153 a,153 b that are identical to the grooves 53 a, 53 b described above.These dummy grooves are engaged by the clamp elements 104, 106, in themanner described above. The proximal end of the dummy prosthesis 150defines an insert cavity 162 with a base recess 164 and plate recess166, all configured to receive the insert component 54.

The dummy prosthesis 150 functions the same as a final or trialprosthesis when mounted within the replication instrument 100. However,the dummy stem 152 does not require the features found on an implantablestem, since the dummy prosthesis 150 is not configured for implantationwithin the patient's bone. Preferably, the stem 152 is about ⅓ thelength of the final prosthesis stem so that the dummy prosthesis is easyto manipulate and fix within the replication instrument.

As explained above, the illustrated embodiment provides a prosthesis forthe humeral aspect of the shoulder joint. Thus, the prosthesis 50 andits components are appropriately dimensioned for implantation within thehumerus bone of the patient. In a specific embodiment, the base portion70 of the insert component 54 has a diameter of 0.5 inches and a heightof 0.183 inches to fit within a comparably dimensioned base recess 64.The plate portion 72 has a width of 0.525 inches, a thickness of 0.1inches, and an overall length of 0.752 inches to fit within a platerecess 66 of the same dimensions. The threaded stem 92 of the fixationscrew 56 has a length of 0.197 inches to pass through the bottom wall 77of the insert portion and into a bore 76 threaded to a depth of 0.175inches. Preferably, the plate portion 72 of the insert is sized to sitsubstantially flush with the platform surface 60 of the prosthesis 50

Furthermore, the components of the prosthesis are formed of acceptablemedical grade materials appropriate for the particular function beingserved by the components. For instance, the stem is formed of a materialappropriate for implantation within a prepared intramedullary canal. Theinsert component and mating component are formed of a biocompatiblematerial appropriate for the mating engagement between these components.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same should be considered asillustrative and not restrictive in character. It is understood thatonly the preferred embodiments have been presented and that all changes,modifications and further applications that come within the spirit ofthe invention are desired to be protected.

For instance, the mating interface between the insert component and themating component can be reversed. Specifically, the tapered bore may beincorporated into the mating component, while the ball portion projectsfrom the insert component. The same modification can be made to themating interface between the humeral head and the mating portion.

In the preferred embodiment, the fixation element is a machine screw;however, other forms of fixation or fastening are contemplated. Forinstance, rather than a screw that requires multiple turns for completefixation, the element can incorporate a rotating locking cam or bayonetmount arrangement. As a further alternative, the fixation element canincorporate a press-in feature in which the element is pressed into thebore and locks in place, such as a spring clip construction. Thefixation element must be capable of achieving a rigid attachment of theinsert component to the stem. Moreover, it is preferred that thefixation element be capable of removal without disturbing or damagingthe implanted stem.

In accordance with the preferred embodiment of the invention, the insertcomponent is removable to facilitate revision or replacement of theangularly adjustable components. In one specific application, the insertcomponent is implemented solely as a trial implant wherein the insertcomponent is removably fixed to the stem to permit positioning of themating component and femoral head in a proper anatomic orientation. Withthe mating component locked in its acceptable position, the insertcomponent can be removed and placed within a replication instrument. Theorientation of the mating component may then be replicated in a finalprosthesis that does not include the insert component.

The present invention provides advantages even if the insert componentis permanently fixed to the stem. Where the final implant includes theinsert component, the insert component may be permanently fixed to theimplanted stem with an appropriate fixation element. This variationstill takes advantage of the ability to establish a final angularorientation of the mating component outside the surgical site.

What is claimed is:
 1. A method for performing a revision of a jointprosthesis having an implant engaged within a bone of the joint and apreviously implanted articulating component fixed to a previouslyimplanted insert component removably mounted to the implant, comprising:removing the previously implanted insert component with the previouslyimplanted articulating component fixed thereto from the implant with theimplant engaged within the bone; determining an angular position of thepreviously implanted articulating component with respect to thepreviously implanted insert after removing the previously implantedinsert component using a replication instrument; replicating thedetermined angular position with a new insert component and a newarticulating component prior to fixing the new articulating component tothe new insert component; fixing the new articulating component to thenew insert component; and mounting the new insert component with the newarticulating component fixed thereto to the implant engaged within thebone.
 2. The method for performing a revision of claim 1, wherein theremoving step includes disengaging a first removable fastener engagingthe previously implanted insert component to the implant.
 3. The methodfor performing a revision of claim 2, wherein the first removablefastener is a screw and the removing step includes advancing a drivingtool through a bore in the previously implanted articulating componentto access the first removable fastener.
 4. The method for performing arevision of claim 1, wherein mounting the new insert component with thenew articulating component fixed thereto comprises: engaging the newinsert component to the implant using a second removable fastener. 5.The method for performing a revision of claim 4, wherein engaging thenew insert component to the implant comprises: advancing the drivingtool through a bore in the new articulating component to access thesecond removable fastener.
 6. The method of claim 1, wherein replicatingthe determined angular position with the new insert component and thenew articulating component comprises: inserting a ball portion of amating component into a tapered bore of the insert; and engaging atapered cylinder portion of the mating component with the newarticulating component.
 7. The method of claim 6, wherein replicatingthe determined angular position with the new insert component and thenew articulating component further comprises: press fitting the ballportion within the tapered bore.
 8. The method of claim 7, whereinreplicating the determined angular position with the new insertcomponent and the new articulating component further comprises:impacting the press fit ball portion within the tapered bore using analignment tool which was used to replicate the determined angularposition.
 9. The method of claim 1, wherein mounting the new insertcomponent with the new articulating component fixed thereto to theimplant engaged within the bone comprises: inserting a first insertportion of the new insert into a first cavity portion of the implant;and inserting a second insert portion of the new insert into a secondcavity portion of the implant, wherein the first insert portion, thefirst cavity portion, the second insert portion, and the second cavityportion are configured such that the new insert can only be mounted in asingle predetermined orientation with respect to the implant.
 10. Themethod of claim 1, wherein mounting the new insert component with thenew articulating component fixed thereto to the implant engaged withinthe bone comprises: inserting a cylindrical portion of the new insertinto a cavity of the implant through a platform plane defined by aplatform surface of the implant, wherein the new insert is configured tomate with the implant in a rotationally keyed configuration whichrotationally fixes the new insert in the cavity at a predeterminedrotational angle.
 11. The method of claim 10, wherein mounting the newinsert component with the new articulating component fixed thereto tothe implant engaged within the bone further comprises: mating aprojecting portion of the new insert with a recess in the implant, therecess having a first opening portion that opens to the platform surfaceand a second opening portion that opens to a side of the implantextending away from the platform surface.
 12. The method of claim 1,wherein removing the previously implanted insert component comprises:positioning a tool between a tab portion of the previously implantedinsert component and a recess in the implant, the recess having a firstopening portion that opens to a platform surface at a proximal portionof the implant and a second opening portion that opens to a side of theimplant extending away from the platform surface, by inserting a portionof the tool into the second opening portion; and using the tool todisengage the previously implanted insert component from the implant.